A lithographic printing plate precursor element is made by coating a support web, with a thermal insulating layer, and then overcoating with a coextensive ink repellent layer. The coextensive ink repellant layer comprises a crosslinked polymeric matrix containing a colloid of an oxide or a hydroxide...http://www.google.com/patents/US6207348?utm_source=gb-gplus-sharePatent US6207348 - Crosslinked polymeric matrix containing a colloid of an oxide or a hydroxide of beryllium, magnesium, aluminum, silicon, gadolinium, germanium, arsenic, indium, tin, antimony, tellurium, lead, bismuth, a transition metal or combinations

A lithographic printing plate precursor element is made by coating a support web, with a thermal insulating layer, and then overcoating with a coextensive ink repellent layer. The coextensive ink repellant layer comprises a crosslinked polymeric matrix containing a colloid of an oxide or a hydroxide of a metal selected from the group consisting of beryllium, magnesium, aluminum, silicon, gadolinium, germanium, arsenic, indium, tin, antimony, tellurium, lead, bismuth, a transition metal and combinations thereof. A photothermal conversion material is present in the ink repellent layer, in a stratum located between the thermal insulating layer and the ink repellent layer, or in both the ink repellent layer and the stratum. The ink repellant layer contains less than 5% hydrocarbon groups by weight.

Images(7)

Claims(35)

We claim:

1. A lithographic printing plate precursor element which comprises:

a) a support web;

b) a thermal insulating layer; and

c) a coextensive ink repellent layer comprising a crosslinked polymeric matrix comprising a colloid of an oxide or a hydroxide of a metal selected from the group consisting of beryllium, magnesium, aluminum, silicon, gadolinium, germanium, arsenic, indium, tin, antimony, tellurium, lead, bismuth, a transition metal and combinations thereof; wherein a photothermal conversion material is present in the ink repellent layer, in a stratum located between the thermal insulating layer and the ink repellent layer, or in both the ink repellent layer and the stratum, wherein the ink repellant layer contains less than 5% hydrocarbon groups by weight.

2. The element of claim 1 wherein the photothermal conversion material is in the coextensive ink repellent layer.

3. The element of claim 1 wherein the lithographic printing plate contains the stratum which comprises the photothermal conversion material and a polymeric binder.

4. The element of claim 3 wherein the stratum comprises carbon dispersed in a cellulosic binder.

6. The element of claim 3 wherein the stratum comprises carbon dispersed in a polyvinylbutyral.

7. The element of claim 6 wherein the polyvinylbutyral is poly(vinylbutyral-co-vinylalcohol-co-vinylacetate)(80%,18%,2%).

8. The element of claim 3 wherein the stratum comprises an IR dye dispersed in a cellulosic binder.

9. The element of claim 1 wherein said support web is a polyester film.

10. The element of claim 1 wherein the support web is an anodized aluminum sheet.

11. The element of claim 1 wherein the insulating layer has a thermal conductivity less than 0.001 cal/(sec)(square cm)(° C./cm).

12. The element of claim 1 wherein the insulating layer comprises a thermoplastic polymeric resin selected from the group consisting of a cellulose acetate propionate, a poly(methyl methacrylate), a polystyrene, a poly(vinyl butyral), and a polycarbonate.

13. The element of claim 1 wherein the insulating layer comprises a polycarbonate.

26. The element of claim 1 wherein the photothermal conversion material is an IR dye.

27. The element of claim 26 wherein the IR dye is 2-{2-{2-Chloro-3-{(1,3-dihydro-1,1,3-trimethyl-2H-benz{e}indol-2-ylidene) ethylidene}-1-cyclohexen-1-yl}-ethenyl}-1,1,3-trimethyl-1H-benz{e}indolium salt of 4-methylbenzenesufonate; or 2-{2-{2-Chloro-3-{(1,3-dihydro-1,1,3-trimethyl-2H-benz{e}indol-2-ylidene) ethylidene}-1-cyclohexen-1-yl}-ethenyl}-1,1,3-trimethyl-1H-benz{e}indolium salt of 4-methylbenzenesufonate.

28. The element of claim 1 wherein the crosslinked polymeric matrix is derived from a crosslinking agent which is an alkoxy silane, an alkyl titanate, an alkyl zirconate or an alkyl aluminate.

29. The element of claim 28 wherein the crosslinking agent is a di, tri, or tetra alkoxy silane.

30. The element of claim 28 wherein the crosslinking agent is aminopropyltriethoxysilane.

31. The element of claim 28 wherein the crosslinking agent is a mixture of dimethyidimethoxysilane and methyltrimethoxysilane.

32. The element of claim 28 wherein the crosslinking agent is glycidoxypropyltrimethoxysilane.

33. The element of claim 28 wherein the coextensive ink repellant layer contains 100 to 5000% of the colloid based on the weight of the crosslinking agent.

34. A method of making a lithographic printing plate comprising:

I) providing an element comprising:

a) a support web;

b) a thermal insulating layer; and

c) a coextensive ink repellent layer comprising a crosslinked polymeric matrix comprising a colloid of an oxide or a hydroxide of a metal selected from the group consisting of beryllium, magnesium, aluminum, silicon, gadolinium, germanium, arsenic, indium, tin, antimony, tellurium, lead, bismuth, a transition metal and combinations thereof; wherein a photothermal conversion material is present in the ink repellent layer, in a stratum located between the thermal insulating layer and the ink repellent layer, or in both the ink repellent layer and the stratum, wherein the ink repellant layer contains less than 5% hydrocarbon groups by weight; and,

II) exposing the element to a laser beam having an intensity greater than 0.1 mW/μ2 for a time sufficient to give a total exposure of 200 mJ/cm2 or greater to form an exposed lithographic printing plate.

35. The method of claim 34 wherein after exposing the element to the laser beam, the exposed lithographic printing plate is directly mounted on a lithographic printing press.

Description

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Ser. No. 08/949,559 filed Oct. 14, 1997 abandoned, entitled, “DIMENSIONALLY STABLE LITHOGRAPHIC PRINTING PLATES WITH A SOL-GEL LAYER” by DeBoer and Fleissig. Reference is made to commonly assigned which is a continuation-in-part of U.S. patent application Ser. No. 09/062,350 filed Apr. 17, 1998 which is a continuation-in-part of U.S. patent application Ser. No. 08/816,287 filed Mar. 13, 1997 now abandoned, entitled, “METHOD OF IMAGING LITHOGRAPHIC PRINTING PLATES WITH HIGH INTENSITY LASER”; and U.S. patent application Ser. No. 08/997,958 filed Dec. 24, 1997, now abandoned, which is a continuation-in-part of U.S. patent application Ser. No. 08/979,916 filed Mar. 13, 1997 now abandoned, entitled, “LITHOGRAPHIC PRINTING PLATES WITH A SOL-GEL LAYER”, each by DeBoer and Fleissig. The disclosure of these related applications is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates in general to lithographic printing plates and with a fountain solution and particularly to lithographic printing plates which do not require wet processing before printing.

BACKGROUND OF THE INVENTION

The art of lithographic printing is based upon the immiscibility of oil and water, wherein the oily material or ink is preferentially retained by the image area and the water or fountain solution is preferentially retained by the non-image area. When a suitably prepared surface is moistened with water and an ink is then applied, the background or non-image area retains the water and repels the ink while the image area accepts the ink and repels the water. The ink on the image area is then transferred to the surface of a material upon which the image is to be reproduced; such as paper, cloth and the like. Commonly the ink is transferred to an intermediate material called the blanket which in turn transfers the ink to the surface of the material upon which the image is to be reproduced.

A very widely used type of lithographic printing plate has a light-sensitive coating applied to an aluminum base support. The coating may respond to light by having the portion which is exposed become soluble so that it is removed in the developing process. Such a plate is referred to as positive-working. Conversely, when that portion of the coating which is exposed becomes hardened, the plate is referred to as negative-working. In both instances the image area remaining is ink-receptive or oleophilic and the non-image area or background is water-receptive or hydrophilic. The differentiation between image and non-image areas is made in the exposure process where a film is applied to the plate with a vacuum to insure good contact. The plate is then exposed to a light source, a portion of which is composed of UV radiation. In the instance where a positive plate is used, the area on the film that corresponds to the image on the plate is opaque so that no light will strike the plate, whereas the area on the film that corresponds to the non-image area is clear and permits the transmission of light to the coating which then becomes more soluble and is removed. In the case of a negative plate the converse is true. The area on the film corresponding to the image area is clear while the non-image area is opaque. The coating under the clear area of film is hardened by the action of light while the area not struck by light is removed. The light-hardened surface of a negative plate is therefore oleophilic and will accept ink while the non-image area which has had the coating removed through the action of a developer is desensitized and is therefore hydrophilic.

Direct write photothermal litho plates are known as the Kodak Direct Image Thermal Printing Plate. However, they require wet processing in alkaline solutions. It would be desirable to have a direct write photothermal litho plate that did not require any processing.

The prior art has tried to produce such plates by a variety of means. All of them fall short of a plate that has high writing sensitivity, high image quality, short roll up, and long run length without any processing.

U.S. Pat. No. 5,372,907 describes a direct write litho plate which is exposed to the laser beam, then heated to crosslink and thereby prevent the development of the exposed areas and to simultaneously render the unexposed areas more developable, and the plate is then developed in conventional alkaline plate developer solution. The problem with this is that developer solutions and the equipment that contains them require maintenance, cleaning, and periodic developer replenishment, all of which are costly and cumbersome.

U.S. Pat. No. 4,034,183 describes a direct write litho plate without development whereby a laser absorbing hydrophilic top layer coated on a support is exposed to a laser beam to burn the absorber to convert it from an ink repelling to an ink receiving state. All of the examples and teachings require a high power laser, and the run lengths of the resulting litho plates are limited.

U.S. Pat. No. 3,832,948 describes both a printing plate with a hydrophilic layer that may be ablated by strong light from a hydrophobic support and also a printing plate with a hydrophobic layer that may be ablated from a hydrophilic support. However, no examples are given.

U.S. Pat. No. 3,964,389 describes a no process printing plate made by laser transfer of material from a carrier film (donor) to a lithographic surface. The problem of this method is that small particles of dust trapped between the two layers may cause image degradation. Also, two sheets to prepare is more expensive.

U.S. Pat. No. 4,054,094 describes a process for making a litho plate by using a laser beam to etch away a thin top coating of polysilicic acid on a polyester base, thereby rendering the exposed areas receptive to ink. No details of run length or print quality are given, but it is expected that an uncrosslinked polymer such as polysilicic acid will wear off relatively rapidly and give a short run length of acceptable prints.

U.S. Pat. No. 4,081,572 describes a method for preparing a printing master on a substrate by coating the substrate with a hydrophilic polyamic acid and then imagewise converting the polyamic acid to melanophilic polyimide with heat from a flash lamp or a laser. No details of run length, image quality or ink/water balance are given.

U.S. Pat. No. 4,731,317 describes a method for making a litho plate by coating a polymeric diazo resin on a grained anodized aluminum litho support, exposing the image areas with a YAG laser, and then processing the plate with a graphic arts lacquer. The lacquering step is inconvenient and expensive.

Japanese Kokai No. 55/105560 describes a method of preparation of a litho plate by laser beam removal of a hydrophilic layer coated on a melanophilic support, in which the hydrophilic layer contains colloidal silica, colloidal alumina, a carboxylic acid, or a salt of a carboxylic acid. The only examples given use colloidal alumina alone, or zinc acetate alone, with no crosslinkers or addenda. No details are given for the ink/water balance or limiting run length.

WO 92/09934 describes and broadly claims any photosensitive composition containing a photoacid generator, and a polymer with acid labile tetrahydropyranyl groups. This would include a hydrophobic/hydrophilic switching lithographic plate composition. However, such a polymeric switch is known to give weak discrimination between ink and water in the printing process.

EP 0 562 952 A1 describes a printing plate having a polymeric azide coated on a lithographic support, and removal of the polymeric azide by exposure to a laser beam. No printing press examples are given.

U.S. Pat. No. 5,460,918 describes a thermal transfer process for preparing a litho plate from a donor with an oxazoline polymer to a silicate surface receiver. A two sheet system such as this is subject to image quality problems from dust and the expense of preparing two sheets.

In related U.S. patent application Ser. No. 08/816,287 filed Mar. 13, 1997, a lithographic printing plate is described in which a support web is coated with an ink absorbing layer which is preferably overcoated with a crosslinked hydrophilic layer having metal oxide groups on the surface. Exposure of the plate to a high intensity laser beam followed by mounting on a press results in excellent impressions without chemical processing. However, the high writing sensitivity which is defined as about 300 mJ/cm2 could still be improved.

It would be desirable to be able to prepare a litho plate that has high writing sensitivity, high image quality, short roll up, and long run length without any processing. The prior art has failed to do this satisfactorily.

SUMMARY OF THE INVENTION

The present invention is a lithographic printing plate in which a metal support web is coated with a thermal insulating layer and this is coated with a photothermal conversion crosslinked hydrophilic layer having metal oxide groups on the surface. Exposure of this plate to a high intensity laser beam followed by mounting on a press results in dimensionally accurate impressions without chemical processing.

The lithographic printing plate precursor element comprises:

a) a support web,

b) a thermal insulating layer

c) a coextensive ink repellent photothermal conversion layer comprising a crosslinked polymeric matrix containing a colloid of an oxide or a hydroxide of a metal selected from the group consisting of beryllium, magnesium, aluminum, silicon, gadolinium, germanium, arsenic, indium, tin, antimony, tellurium, lead, bismuth, a transition metal and combinations thereof, wherein a photothermal conversion material is present in the ink repellent photothermal conversion layer, in a stratum located between the thermal insulating layer and the ink repellent photothermal conversion layer, or in both the ink repellent photothermal conversion layer and the stratum.

An added embodiment of this invention is a method of making a lithographic printing plate comprising:

I) providing an element comprising:

a) a support web,

b) a thermal insulating layer

c) a coextensive ink repellent photothermal conversion layer comprising a crosslinked polymeric matrix containing a colloid of an oxide or a hydroxide of a metal selected from the group consisting of beryllium, magnesium, aluminum, silicon, gadolinium, germanium, arsenic, indium, tin, antimony, tellurium, lead, bismuth, a transition metal and combinations thereof; wherein a photothermal conversion material is present in the ink repellent photothermal conversion layer, in a stratum located between the thermal insulating layer and the ink repellent photothermal conversion layer, or in both the ink repellent photothermal conversion layer and the stratum; and,

II) exposing the element to a laser beam having an intensity greater than 0.1 mW/μ2 for a time sufficient to give a total exposure of 200 mJ/cm2 or greater to form an exposed lithographic printing plate. A further advantage of this embodiment is that after exposing the element to the laser beam, the exposed lithographic printing plate is directly mounted on a lithographic printing press.

DETAILED DESCRIPTION OF THE INVENTION

The lithographic printing plate element of this invention contains at least three structural components, a support web, a thermal insulating layer, and a top coextensive melanophobic, i.e., ink repellent, photothermal conversion layer. A photothermal conversion material is located either in the top layer or in a stratum between the insulating layer and top layer. The top layer is composed of a crosslinked polymeric matrix containing a colloid of an oxide or a hydroxide of a metal selected from the group consisting of beryllium, magnesium, aluminum, silicon, gadolinium, germanium, arsenic, indium, tin, antimony, tellurium, lead, bismuth, a transition metal and combinations thereof.

As used herein, the term “melanophilic” is Greek for ink-loving, i.e., “ink receptive”, and the term melanophobic is Greek for ink-fearing, i.e., “ink repellent”. Since most conventional printing inks are linseed oil based and are used with an aqueous fountain solution in conventional lithographic printing, melanophilic will usually coincide with “oleophilic” and melanophobic will usually coincide with “hydrophilic”.

Support Web

The support web for this invention can be a polymer, metal or paper foil, or a lamination of any of the three. The term “support web” as used herein is intended to mean any substrate, sheet, film or plate material having a composition and physical dimensions commonly used as substrates in lithography. The thickness of the support web (hereinafter identified as “support”) can be varied, as long as it is sufficient to sustain the wear of the printing press and thin enough to wrap around the printing form. A preferred embodiment uses a polyester film, such as a polyethylene terephthalate film in a thickness from 100 to 200 microns as the support web. In another preferred embodiment, the support web is an aluminum sheet from 100 to 500 microns in thickness; and more preferably is an anodized aluminum sheet and particularly a grained anodized aluminum sheet. The support should resist stretching so the color records will register in a full color image. The support may be coated with one or more “subbing” layers to improve adhesion of the final assemblage. The back side of the support may be coated with antistat agents and/or slipping layers or matte layers to improve handling and “feel” of the resulting litho plate.

Thermal Insulating Layer

The thermal insulating layer is composed of a material that has a heat conduction rate significantly lower than the metal support. The thermal conductivity of the insulating layer should be less than 0.001 cal/(sec)(square cm)(° C./cm). In addition the insulating layer is chosen to be insoluble in the solvents used for the overcoat. The material for the insulating layer is also chosen to adhere well to the metal support, and to provide good adhesion to the overcoat. In addition, the cohesive strength of the insulating layer must be high enough, for example having a tensile strength greater than 50 kilograms per square centimeter to provide long run lengths on the printing press without cohesive failure of the insulating layer. Exemplary materials for the insulating layer are the family of thermoplastic polymeric resins, such as cellulose acetate propionates, poly(methyl methacrylates), polystyrenes, polyvinylbutyrals, and the polycarbonates. Typical resins of these types are: Butvar B76 poly(vinylbutyral-co-vinylalcohol-co-vinylacetate) (80%,18%,2%) from Monsanto; cellulose acetate propionate 382-20 from Eastman Chemicals; Lexan 141 polycarbonate from General Electric Corporation; and polyvinylacetate from Aldrich Chemicals.

Top Melanophobic Layer

The top coextensive melanophobic, i.e., ink repellent or hydrophilic, photothermal conversion layer is composed of a crosslinked polymeric matrix containing at least a colloid of an oxide or a hydroxide of beryllium, magnesium, aluminum, silicon, gadolinium, germanium, arsenic, indium, tin, antimony, tellurium, lead, bismuth, a transition metal or combinations thereof. In an embodiment of this invention the top layer additionally contains a photothermal conversion material as described below.

In the unexposed areas, the hydrophilic layer is intended to be wet effectively by the aqueous fountain solution in the lithographic printing process, and when wet, to repel the ink. In addition, it is useful if the hydrophilic layer is somewhat porous, so that wetting is even more effective. The hydrophilic layer must be crosslinked if long printing run lengths are to be achieved, because an uncrosslinked layer will wear away too quickly. The ink repellent or hydrophilic layer is a sol-gel layer which is a crosslinked polymeric matrix containing a colloid of an oxide or a hydroxide of a metal selected from the group consisting of beryllium, magnesium, aluminum, silicon, gadolinium, germanium, arsenic, indium, tin, antimony, tellurium, lead, bismuth, a transition metal and combinations thereof. Many such crosslinked hydrophilic layers are available. Those derived from di, tri, or tetra alkoxy silanes or titanates, zirconates and aluminates are particularly useful in this invention. Examples are colloids of hydroxysilicone, hydroxylaluminum, hydroxyltitanium and hydroxyzirconium. Those colloids are formed by methods fully described in U.S. Pat. Nos. 2,244,325; 2,574,902; and 2,597,872. Stable dispersions of such colloids can be conveniently purchased from companies such as the DuPont Company of Wilmington, Del. It is important that the hydrophilic layer have a strong affinity for water. If the hydrophilic layer does not hold enough water, the background areas may carry some ink, commonly referred to as “scumming” of the litho plate. To compensate for this problem, the press operator may have to increase the amount of fountain solution fed to the printing form, and this, in turn, may lead to emulsification of the ink with the fountain solution, resulting in a mottled appearance in solid dark areas. The severity of the problem will depend on the actual ink and fountain solution as well as the press that is being used, but, in general, the more affinity the background of the plate has for water, the less printing problems will be. In this invention, it has been found that an overcoat of metal colloids crosslinked with a crosslinker containing ionic groups helps to hold water and improves the printing performance. In a preferred embodiment of the invention the metal colloid is colloidal silica and the crosslinker is N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride. For the same reason, the hydrophilic layer is most effective when it contains a minimum amount of hydrophobic groups such as methyl or alkyl groups. The thickness of the crosslinking and polymer forming layer may be from 0.05 to 1 micron in thickness, and most preferably from 0.1 to 0.3 microns in thickness. The amount of silica added to the layer may be from 100 to 5000% of the crosslinking agent, and most preferably from 500% to 1500% of the crosslinking agent. Surfactants, dyes, colorants useful in visualizing the written image, and other addenda may be added to the hydrophilic layer, as long as their level is low enough that there is no significant interference with the ability of the layer to hold water and repel ink. Descriptions of preferred embodiments of the hydrophilic layer are given in cross referenced U.S. patent application Ser. No. 08/997,958, filed Dec. 24, 1997 entitled, “LITHOGRAPHIC PRINTING PLATES WITH A SOL-GEL LAYER”. Such preferred hydrophilic layers include layers prepared from Nalco 2326, 5 nm ammonia stabilized colloidal silica, (from the Nalco Corporation, Naperville, Ill.); tetrabutyltitanate; a mixture of colloidal alumina (Dispal 18N4-20) with hydrolyzed tetraethylorthosilicate; a mixture of tetraethylorthosilicate with hydrochloric acid; zirconium butoxide; and the like. Preferred hardeners used in these hydrophilic layers include: 3-aminopropyltriethoxysilane; a mixture of dimethyl dimethoxysilane and methyl trimethoxysilane sold as Z-6070 by the Dow Corning Company; glycidoxypropyltrimethoxysilane; and the like.

Photothermal Conversion Material

The photothermal conversion material is present either in the melanophobic, the top ink repellent, photothermal conversion layer, in a stratum located between the thermal insulating layer and the top ink repellent layer, or in both the top ink repellent layer and the stratum. When the stratum is present it functions in conjunction with the top layer as a photothermal conversion layer.

The photothermal conversion material absorbs laser radiation and converts it into heat. It converts photons into heat phonons. To do this it must contain a non-luminescent absorber. Such an absorber may be a dye, a pigment, a metal, or a dichroic stack of materials that absorb by virtue of their refractive index and thickness. In addition to heating the layer, the absorber must have the property of causing the image areas of the printing plate to become melanophilic after exposure to the laser. Since most conventional printing inks are linseed oil based, melanophilic will usually coincide with oleophilic. A useful form of particulate radiation absorbers containing a mixture of absorbing dye and melanophilic binder can be made the evaporative limited coalescence process as described in U.S. Pat. No. 5,234,890, hereby incorporated by reference. Examples of dyes useful as absorbers for near infrared diode laser beams may be found in U.S. Pat. No. 4,973,572, hereby incorporated by reference. Preferred infrared (IR) absorbing dyes for use in this invention are 2-{2-{2-Chloro-3-{(1,3-dihydro-1,1,3-trimethyl-2H-benz{e}indol-2-ylidene)ethylidene}-1-cyclohexen-1-yl}-ethenyl}-1,1,3-trimethyl-1H-benz{e}indolium salt of 4-methylbenzenesufonate; and 2-{2-{2-chloro-3-{(1,3-dihydro-1,1-dimethyl-3-sulfonatopropyl-2H-benz {e}indol-2-ylidene)ethylidene}-1-cylcohexen-1-yl}ethenyl}-1,1-dimethyl-3-sulfonatopropyl-1H-benz{e}indolium sodium salt. In a preferred embodiment of the invention the absorber is a pigment. In a more preferred embodiment of the invention the pigment is carbon, particularly sulfonic acid surface modified submicron carbon particles. The size of the particles should not be more than the thickness of the layer. Preferably, the size of the particles will be half the thickness of the layer or less, from about 0.1 micron to about 0.5 micron.

The photothermal conversion material may reside throughout the topmost hydrophilic, melanophobic (ink repellent) layer, or it may reside in a separate stratum, or photothermal conversion layer, between the topmost layer and the insulating layer below, provided that the photothermal conversion material is “thermally close” to the topmost layer. It will be understood by those skilled in the art, that the term “thermally close” means that the photothermal conversion material must deliver a substantial portion of its heat to the topmost layer in order to switch the exposed areas of the printing plate from melanophobic to melanophilic.

If a binder is used to hold a dye or pigment in the stratum, photothermal conversion layer, it may be chosen from a large list of film forming polymers. Useful polymers may be found in the families of polycarbonates, polyesters, polyvinylbutyrals, and polyacrylates. Chemically modified cellulose derivatives are particularly useful, such as nitrocellulose, cellulose acetate propionate, and cellulose acetate. Exemplary polymers may be found in U.S. Pat. Nos. 4,695,286; 4,470,797; 4,775,657; and 4,962,081, hereby incorporated by reference. Preferred photothermal conversion layers of this type includes layers comprising carbon dispersed in a cellulosic binder, and particularly layers comprising carbon dispersed in nitrocelulose. Also preferred are strata comprising an IR dye dispersed in a cellulosic binder. The preferred thermal conversion layers may also contain a non-cellulosic co-binder in addition to the cellulosic binder. Useful co-binders include the family of thermoplastic polymeric resins identified above in connection with the insulating layer. A particularly advantageous co-binder is a polyvinylbutyral such as Butvar B76 poly(vinylbutyral-co-vinylalcohol-co-vinylacetate)(80%,18%,2%) from Monsanto.

Typically the layers of the element of this invention are coated on the support, or previously coated intermediate layers, by any of the commonly known coating methods such as spin coating, knife coating, gravure coating, dip coating, or extrusion hopper coating. Surfactants may be included in the coated layers to facilitate coating uniformity. A particularly useful surfactant for coated polymer layers is Zonyl FSN, a surfactant manufactured by the DuPont Company of Wilmington, Del.

Method of Use

The process for using the resulting lithographic plate comprises the steps of 1) exposing the plate to a focused laser beam in the areas where ink is desired in the printing image, and 2) employing the plate on a conventional lithographic printing press. No heating, process, or cleaning is needed before the printing operation. A vacuum cleaning dust collector may be useful during the laser exposure step to keep the focusing lens clean. Such a collector is fully described in U. S. Pat. No. 5,574,493.

The laser used to expose the lithoplate of this invention is preferably a diode laser, because of the reliability and low maintenance of diode laser systems, but other lasers such as gas or solid state lasers may also be used. In the method for making the lithographic printing plate described above, it has been found that by exposing these elements to a focused laser beam having an intensity greater than 0.1 mW/μ2 for a time sufficient to give a total exposure of about 200 milliJoules/cm2 or greater, the efficiency of the operation improves and better printing steps are achieved with lower laser exposure energy. Good printing steps are defined as those having a uniform reflection optical density greater than 1.0. This improvement in efficiency is unexpected because it has generally been found in exposure of lithographic printing plates from a film negative that the same exposure level is required, that is, the same amount of joules per square centimeter, regardless of the intensity of the exposure lamp. In a typical mode of operation, the printing plate of this invention is exposed to a focused diode laser beam emitting in the infrared spectral region, such as at a wavelength of 830 nm, on an apparatus similar to that described in U.S. Pat. No. 5,446,477, with exposure levels of about 600 mJ/cm2, and intensities of the beam of about 3 mW/μ2. In this mode of operation the laser beam typically is modulated to produce a halftone dot image. After imaging exposure, the imaged plate of this invention is directly mounted on a conventional lithographic printing press, such as an ABDick press, without any intermediate processing steps, and the conventional printing process is initiated.

The following examples show the improvement in writing speed by the use of the insulating layer of this invention but are not intended to be limited thereby.

EXAMPLE 1

A grained, anodized aluminum support was coated with a 5% solution of Butvar B76 poly(vinyl-co-butyral-co-alcohol-co-acetate)(80%,18%,2%)(Monsanto) in methyl isobutyl ketone, using a 2 ml. knife. When dry, the plate was overcoated with a solution of 15 g. of colloidal silica (Nalco 2326, 5 nm colloidal silica, ammonia stabilized, from the Nalco Corporation, Naperville, Ill.), 85 g. water, 0.50 g. of 10% Zonyl FSN surfactant in water (DuPont Wilmington, Del.), 1 g. of carbon (Cabojet 300, a 15% water dispersion of carbon from the Cabot Corporation, Bellerica, Mass.), and 0.25 g. of 3-aminopropyltriethoxysilane, added by drops with stirring. A 1.5 ml. knife was used for the coating. The dry plate was then baked at 100° C. for 15 minutes.

The plate was then exposed to a focused diode laser beam at 830 nm wavelength on an apparatus similar to that described in U.S. Pat. No. 5,446,477. The exposure level was about 600 mJ/square cm, and the intensity of the beam was about 3mW/square micron. The laser beam was modulated to produce a stepwedge pattern, where each step had 6/256 less power than the previous step. After exposure the plate was directly mounted on an ABDick press with no intermediate developing steps, and several hundred impressions were made. The required exposure was defined by the last solid ink density step that was printed. In this example 20 steps were printed when the plate was exposed at 400 rpm.

EXAMPLE 2

Example 1 was repeated but the Butvar was replaced with cellulose acetate propionate 382-20 (Eastman Chemicals, Kingsport, Tenn.). In this example 18 steps were printed when the plate was exposed at 400 rpm.

EXAMPLE 3

Example 1 was repeated but the Butvar was replaced with polyvinylacetate (Aldrich Chemicals). In this example 22 steps were printed when the plate was exposed at 400 rpm.

EXAMPLE 4

Example 1 was repeated but the Butvar was replaced with Lexan 141 polycarbonate (General Electric Corporation) and the solvent used was dichloromethane. In this example 31 steps were printed when the plate was exposed at 400 rpm.

Control 1

Example 1 was repeated, but no insulating layer was coated on the aluminum. In this example no steps were printed when the plate was exposed at 400 rpm. At 100 rpm a few faint steps were seen to be printed.

EXAMPLE 5

A grained anodized aluminum support was coated at 30 g per square meter with a solution of 4 g of nitrocellulose (from Herculese Corporation—70% nitrocellulose moistened with 30% propanol has a viscosity of 1000-1500 cps), and 1.5 g of Butvar B76 in 266 ml of methylisobutylketone with 1 g of added 3-aminopropyltriethoxylsilane as a crosslinking agent. After drying, the coating was baked at 100° C. for an hour to effect crosslinking. The clear, crosslinked layer was overcoated at 30 g per square meter with a solution of 4 g of the above nitrocellulose and 1.5 g Butvar B76 in 266 ml of methylisobutylketone with 1 g of added 3-aminopropyltriethoxylsilane and 1.3 g of 2-{2{2-Chloro-3-{(1,3-dihydro-1,1,3-trimethyl-2H-benz{e}indol-2-ylidene) ethylidene}-1cyclohexen-1-yl}-ethenyl}-1,1,3-trimethyl-1H-benz {e}indolium salt of 4-methylbenzenesufonate. When dry, the layer was overcoated with a solution of 30 g of Nalco 2326 colloidal silica, 70 g water, 0.5 g of the surfactant nonylphenoxypolyglycidol, and 0.5 g 3-aminopropyltriethoxylsilane, added by drops with stirring. The layer was allowed to dry, and then the assembly was baked at 100° C. for an hour to produce a printing plate element.

The printing plate element was exposed to a focused diode laser beam as described in Example 1. After exposure the plate was directly mounted on an ABDick lithographic printing press and several hundred impressions were made more than 15 steps were observed when the plate was exposed at 400 rpm.

The invention has been described in detail, with particular reference to certain preferred embodiments thereof, but it should be understood that variations and modifications can be effected within the spirit and scope of the invention.

Aluminum substrate, an image-recording layer and a hydrophilic film, the aluminum substrate being subjected to an electrochemical surface roughening treatment in an aqueous solution comprising hydrochloric acid and provided with the